Pros
Job Security: You really don't feel like your job is threatened when working here. Smart Colleagues: The people working at Wolfram Research are smart. Really smart. They almost all have at least their masters and you can learn a ton from them. Creative Freedom: Since you may be the only developer on a project (or one of a few) you can implement things with a good amount of creative freedom. (Can be good or bad)
Cons
Compensation and Benefits: The combination of these two factors is pretty depressing. The pay is FAR below market value yet the benefits are the most expensive that I have seen. Very disheartening. Project Management: There is a lot to be desired about project management. As a developer, you will spend an exorbitant amount of time tracking down things to implement the smallest features because no assessments are done for features. Issues are created with no description. Features are requested with no documentation. You have no clue what systems will be using the feature you are adding. Antiquated Tech and Bad Practices: This was a very surprising thing that I found coming in. We were using very old technologies and using them incorrectly. Many anti-patterns used and refusal to fix them. Just a pile of bugs in your queue as a result. Egos: There is not a lot of camaraderie. Very easy to be thrown under the bus or get a sarcastic remark when asking for help. Also, the founder and CEO is very condescending. If he ever finds a bug, please expect a strongly worded email or a meeting full of profane language. Not very comforting on day 1 as a new hire.